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A Comparative Study Using Electromyography to Assess Hand Exercises For Rehabilitation After Ulnar Nerve Decompression
Colton G Boudreau, MSc, Joseph Corkum, MD, Ian Grant, MD and David Tang, MD, Dalhousie University, Halifax, NS, Canada

Background: Ulnar nerve (UN) entrapment is a common peripheral neuropathy that can lead to loss of both sensory and motor function of the hand. Surgical release is the mainstay of treatment for ulnar neuropathies, but post-operative rehabilitation of UN-innervated muscles has received little study. This study uses electromyography to compare four exercises in healthy participants in order to determine which exercises maximize activation of specific muscles.

Methods: Surface electromyography (EMG) was used to assess the activation of ulnar innervated intrinsic and extrinsic muscles during four exercises in ten healthy participants. Intrinsic muscles were abductor digiti minimi (ADM) and first dorsal interosseous (FDI), while flexor carpi ulnaris (FCU) was studied for extrinsic activation. Maximum volitional EMG activity was measured during finger abduction against taped digits. Exercises included constant rotation of boading balls, squeezing a stress ball or 100 pound grip device every second, and alternating finger abduction/adduction against a rubber band every second. Percent activation of each muscle during exercises was calculated by dividing the root mean square (RMS) EMG amplitude by the maximum volitional amplitude for that muscle.

Results: Repetitive rubber band resistance abduction/adduction shows significantly increased activation in ADM compared to all other exercises tested. For FDI, rubber band resistance and grip device squeezing showed similar results, both of which were significantly more effective than other exercises. Extrinsic muscle FCU showed similar activation with squeezing a stress ball and a grip device, both of which were significantly more effective than other exercises.

Conclusions: Our findings indicate that rubber band resistance finger abduction/adduction is superior in terms of muscle activation as compared to all other tested exercises. Grip device squeezing showed similar activation for the FDI, but also showed significant recruitment of FCU. Therefore, to best target the intrinsic hand muscles without fatiguing extrinsic muscles, the inexpensive, practical and easy-to-learn rubber band resistance exercise would be most beneficial in rehabilitation after ulnar nerve release.

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